Fangirl is a slang word that arose with online fan communities, or fandoms. There's a fandom for everything from Sherlock to My Little Pony, and the word can be a noun or verb, as in, "I'm a Dr. Who fangirl," or "I saw David Tennant and totally fangirled." (For the record, we would too.) Rainbow Rowell created the character of Cath after becoming obsessed with Harry Potter fanfiction herself, which is why Cath's fandom is Simon Snow and not, say, ponies. As the author of the most popular Simon Snow fanfic, Cath's not just a fangirl; she's the fangirl. So because of this, she's not just a nerd—she's queen of the nerds, but college is about to knock her off her throne a bit.